FIG. 1 is a system architecture diagram of an LTE system in a 3GPP cellular mobile family system. The LTE system includes: a Mobility Management Entity (MME) and a Serving Gateway (SGW) at a core network side, and a UE (or called terminal) and an eNodeB (called eNB for short) at a radio access network side, and there is a Uu air interface or air interface between the UE and the eNB. There is an S1-MME (S1 for the control plane) interface between the eNB and the MME, and there is an S1-U interface between the eNB and the SGW, and there are an X2-U (X2-User plane) interface and an X2-C (X2-Control plane) interface between eNB s.
FIG. 2 (a) to FIG. 2(d) are diagrams illustrating protocol stack architectures of control planes and user planes between a UE and an eNB and a core network (MME and SGW), and protocol stack architectures of a control plane and a user plane between eNBs. Herein, a Uu air interface Media Access Control (MAC) layer protocol and a Physical Layer (PHY) protocol are contents relevant to subsequent contents of the embodiments of the present disclosure. The MAC layer mainly provides data transmission for an upper logic channel and is responsible for allocating uplink and downlink radio resources, to complete functions of Hybrid Automatic Repeat Request (HARQ), scheduling, priority processing, multiplexing (MUX), demultiplexing and the like. The PHY layer mainly provides PHY-relevant signal processing, transmission means and air interface signal conversion for data packets (MAC Protocol Data Units (PDUs)) from a transmission channel. In addition, a Radio Link Control (RLC) layer on an upper layer of the Uu air interface is mainly used for providing segmentation and retransmission service for user and control data. A Packet Data Convergence Protocol (PDCP) layer is mainly used for completing transfer of user data to the RRC layer or an upper layer of a user plane. The RRC layer is mainly used for completing broadcast, paging, radio resource control connection management, radio bearer control, mobility function, terminal measurement report and control, and the like. Relevant protocol specifications of the LTE can be queried in a public website of a 3GPP.
Before a Rel-10 version of the LTE system, a terminal and an eNB can only perform uplink and downlink communications in a cell configured on one licensed carrier, to achieve data transmitting and receiving on a single licensed carrier. At this time, the eNB configures only one serving cell for the terminal. Starting from the Rel-10 version of the LTE system, to improve a peak rate of the terminal and dynamically coordinate and utilize radio resources between multiple licensed carrier cells, the terminal and the eNB can perform uplink and downlink communications in cells configured on multiple licensed carriers, to achieve data transmitting and receiving on the multiple licensed carriers. At this time, the eNB configures multiple serving cells for the terminal: one primary serving cell (Pcell) (serving cell uniquely responsible for Physical Uplink Control Channel (PUCCH) feedback) and multiple secondary serving cells (Scell) (serving cell at least having a Physical Downlink Shared Channel (PDSCH) and/or a Physical Uplink Shared Channel (PUSCH) for data transmission). That is an LTE Carrier Aggregation (CA) technology. The current existing art is temporarily limitative of aggregation of licensed carriers, and the terminal maximally supports aggregation of five licensed carriers, and a maximum aggregation bandwidth is 5×20M=100M.
Due to relative shortage of licensed carrier resources (required to be competitively purchased by multiple operators) in a licensed band of the LTE system, and since homogeneous deployment networking of a macro cell under a macro eNB cannot satisfy increasing demands for large service traffic of an LTE user, LTE operators expect to develop and utilize unlicensed carrier resources (not required to be competitively purchased by multiple operators and can be freely competed, preempted and used by multiple operators) in an unlicensed band, and service hot spots, such as densely-populated regions, are covered by heterogeneous deployment networking of a micro cell where a micro eNB or a Low Power Node (LPN) is used. FIG. 3(a) is a diagram where two macro cells that have substantially the same uplink and downlink radio coverage and are located on two different adjacent licensed carriers in the same licensed band respectively are configured into a CA operation. A UE can perform uplink and downlink communications simultaneously with macro cells on two licensed carriers within an effective coverage range as to achieve data transmitting and receiving on dual licensed carriers. On the basis of FIG. 3(a), two LPN micro cells are added in FIG. 3(b), and are located on two different unlicensed carriers in an unlicensed band respectively, and keep synchronous in a time sequence relation with two macro cells in FIG. 3(a) through ground optical fiber coordination. Macro cells on two licensed carriers and micro cells on two unlicensed carriers can be configured together into a CA operation theoretically. The UE can perform uplink and downlink communications with the macro cells on the two licensed carriers and the micro cells on the two unlicensed carriers simultaneously within the effective coverage range thereof, to achieve data transmitting and receiving on multiple carriers.
FIG. 4 is a working architecture of LTE pure-licensed CA. When an eNB or a UE serves as a transmitter, N parallel HARQ entities are configured in an MAC protocol entity, and N HARQ data packets (or referred to as MAC PDUs) generated under a specific Transmission Time Interval (TTI) (i.e., TTI for data scheduling of the eNB) are converted into specific physical waveform signals of the LTE finally by means of a series of relevant processing (such as channel coding, modulation, and resource block adaptive mapping and the like) of a PHY entity, and then are transmitted out on N licensed carriers. A UE or an eNB serving as a receiver performs opposite processing through an MAC and/or a PHY entity. Here, a unique Pcell and N−1 Scells are all configured on the licensed carriers.
FIG. 5 is a working architecture of a CA including an LTE unlicensed carrier. When an eNB or a UE serves as a transmitter, N parallel HARQ entities are configured in an MAC protocol entity. However, some of them are traditional HARQ entities (the same as the HARQ entities in FIG. 4) serving licensed carriers, whilst the other are U-HARQ entities (required to modify and enhance characteristics of the unlicensed carriers for the traditional HARQ entities) serving unlicensed carriers. N generated HARQ data packets (or MAC PDUs) are converted into specific physical waveform signals of the LTE finally by means of a series of relevant processing (such as channel coding, modulation, and resource block adaptive mapping and the like) of a PHY entity, and some of them are transmitted out on the licensed carriers, whilst the other are transmitted out on the unlicensed carriers. Likewise, PHY and U-PHY entities are distinguished here to identify difference from a traditional PHY entity. Here, there are still a Pcell on a unique licensed carrier and Scells on multiple licensed carriers as well as U-Scells on multiple unlicensed carriers.
Since resources on unlicensed carriers in a physical local region are shared by multiple eNBs and/or WIFI AP nodes of multiple identical operators and/or different operators, each eNB needs to monitor whether a detection channel is busy or clear in a Listen Before Talk (LBT) manner, and then attempts to preempt channel resources on unlicensed carriers. For example, in the same serving region, an eNB1 of an operator A configures CA: Pcell1+U-Scell for an own user UE1, and an eNB2 of an operator B configures CA: Pcell2+U-Scell for an own user UE2; Pcell1 and Pcell2 are located on licensed carriers of the operator A and the operator B respectively, and there are no problems of interference collision and channel resource sharing therebetween. However, U-Scell is located on the same unlicensed carrier, and at this time, every time the eNB of the operator A and/or B wants to transmit data on U-Scell, the eNB must monitor to detect whether the unlicensed carrier is occupied by other nodes (eNB, WIFI AP, UE or the like). For example, when the eNB1 performs Clear Channel Assessment (CCA) detection at a cycle period to determine that receiving energy on a full bandwidth of the unlicensed carrier is greater than a threshold, it is shown that the unlicensed carrier has been occupied, and the eNB1 cannot preempt a channel resource on the unlicensed carrier at this time. Then, the eNB1 usually backs off for a period of time, and waits for a next cycle time, and then executes CCA for the next time to attempt to preempt the resource on the unlicensed carrier.
A full bandwidth CCA energy detection and time backoff avoidance mechanism under a fixed configuration of a cell bandwidth on the above-mentioned unlicensed carrier has obvious technical defects. Supposed that a full bandwidth of a U-Scell on an unlicensed carrier is 20M, if the total interference energy detected by an eNB through CCA downlink is greater than a threshold, the eNB cannot know how the interference energy is distributed within the full bandwidth of 20M. For example, interference energy detected within a high 10M sub-bandwidth may be large whilst interference energy detected within a low 10M sub-bandwidth may be small, or interference energy detected within a smaller bandwidth, i.e., 5M sub-bandwidth in the 20M is small, which shows that unlicensed carrier resource on the sub-bandwidth can be preempted and used by the eNB. However, the eNB also needs to back off to a next CCA time (usually, a delay in an ms level), thus resulting in the waste of bandwidth resources and increasing a transmission delay of data packets.